type: rule
status: active
timestamp: 2026-06-25
tags: [rule, scope, build-or-buy, anti-reinvention]

Don't rebuild software that already exists completely free

Don't rebuild software that exists free

Don’t rebuild free software

Rule

Do NOT build software that already exists completely free elsewhere.

This applies to userscripts, browser extensions, CLIs, web apps, libraries, and APIs.

Before building anything that mirrors an existing tool’s behavior:

  1. Search. Chrome Web Store, AMO, Greasyfork, GitHub, npm. Did someone already ship this and put it on a free tier with no paywall, no rate-limited “free for personal use” gotcha, no telemetry surcharge?
  2. If yes → STOP. Use theirs. Add a one-line pointer in knowledge/services/ if it’s worth referencing later.
  3. If no, or if the existing one has a paywall on a feature we need → build. Document the paywall / gap in the new project’s README so future agents know why this exists.

Exception: paywalled features

The rule is “no rebuilding completely free software”. If the existing tool’s free tier is missing a feature that the paid tier has — and we want that feature — building a free alternative IS allowed. Examples that would qualify:

When invoking the exception: name the specific paywalled feature in the new project’s README’s “Why this exists” section. “There’s already X” isn’t a sufficient justification on its own — the paywall is.

Why

When in doubt

Ask the user the explicit question: “There’s already a free X that does this. Build anyway, or skip?” Don’t assume the user wants a clone just because they pointed at an extension and said “make this”.

What to do instead when the rule blocks a build

Cross-refs


Edit on GitHub · Back to index